In a Long Time Evolution (LTE) radio network, a user equipment (UE) communicates with one or multiple core networks (CNs) through a Radio Access Network (RAN). RAN coverage is divided into geographic areas of cell areas. Each cell area is served by an evolved NodeB (eNodeB or eNB for short). That is, the eNodeB provides radio coverage in the cell area. The eNodeB communicates with a UE in a cell through a radio air interface.
As shown in FIG. 1, in air interface protocol architecture of LTE, a user-plane protocol stack is used to transmit service data between a UE and an eNodeB. The user-plane protocol stack includes a physical (PHY) layer, a Media Access Control (MAC) layer, a Radio Link Controller (RLC) layer, and a Packet Data Convergence Protocol (PDCP) layer. The PHY layer implements functions such as modulation and encoding of a channel, frequency expansion, and transmission channel multiplexing; the MAC layer mainly implements functions of access control, mapping from a logical channel to a transmission channel, resource scheduling, and hybrid retransmission; the RLC layer implements functions of retransmission mode selection, an automatic repetition request, and encryption; the PDCP layer implements functions of converging and converting of data packets of different formats.
Currently, a relay node is introduced to an LTE-Advanced (LTE-A) specification, and multi-hop transmission exists between a UE and an eNodeB. As shown in FIG. 2, in an LTE-A network where a relay node is introduced, an air interface link from the UE to a directly attached access relay node may be called an access link, and an air interface link from the access relay node to the eNodeB may be called a relay link. Multiple intermediate relay nodes may exist between the access relay node and the eNodeB. Therefore, the relay link may include multiple links.
At present, service data transmission from the UE to the eNodeB may use a user-specific based data transmission mode, or may also use a tunnel-based data transmission mode.
Using the user-specific based data transmission mode to implement the service data transmission from the UE to the eNodeB means establishing a dedicated data bearer for a service of a specific UE in the relay link and the access link respectively so as to complete multi-hop transmission of user service data of the UE, as shown in FIG. 3a. In addition, as a dedicated bearer is established for the UE at each hop in UE-specific based data transmission, the relay node needs to schedule these bearers of the UE at each hop to implement data transmission of these bearers, as shown in FIG. 3b. 
As shown in FIG. 3c, using the tunnel-based data transmission mode to implement the service data transmission means establishing a tunnel bearer in the relay link. Data of multiple users may be converged in a same tunnel bearer for transmission. Data encapsulation and de-encapsulation of the tunnel are performed at network nodes of both sides, such as the access relay node and the eNodeB, of the tunnel. An intermediate relay node only transparently forwards tunnel data. In addition, a protocol stack layer for data forwarding corresponds to a tunnel encapsulation layer.